In the handling of volatile fluids, toxic and/or flammable gases, in a conduit flow system, safety standards require that valves which control the flow of material through the conduit system possess safety redundancies for insuring control as well as requiring vent means for gases which have been trapped by the valve structure which controls flow. It has been a conventional practice to provide two separate valves in series between the intake and outlet. Residue material between the trapped closed valves presented an undesirable and unsafe condition in the system because leakage of such material into the surrounding work environment could be hazardous. Thus, it was further required by safety standards to tap the conduit between the two serial valves to provide a leaching conduit to vent residual material for dispersal into the atmosphere. In this leaching conduit was yet another valve independently operated from the two serial valves which controlled the opening and closing of the vent system.
In gas burner systems a valve arrangement of this type is known as a "double block and vent system". Several drawbacks were found to exist with the foregoing valve system due to inherent deficiencies of the separate valve elements to cooperatively interact with each other in providing a safe and efficient means of controlling fluid flow. One such problem exists with the control of the serial valves. Where each serial valve is independently operated, the user is faced with a requirement for three separate actuator means to control a simple on/off function. In many instances, the system might inadvertently leach pressurized fluid from the incoming source due to the imprecision in the sequencing of the valves. Further, sequencing of valves is complicated by industry safety standards which may require that individual valves themselves possess redundancy in the seating means. Moreover, it is desirable that the seating means be sequenced to seat and unseat in a specific staggered manner. Hence, the problem of efficiently controlling the precise movements can become extremely complicated when one is utilizing three separate valves and actuators to accomplish a single on/off function.